ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 8

SO 3 H group on the FPTFS surface. The maximum adsorption (116 mg g -1 ) of
Cd 2+ onto FPTFS occurred at pH 7.0. The equilibrium was established in 3 h.
The adsorption capacity decreased with the increasing ionic strength,
indicating that electrostatic interaction and surface complexation are very
important steps on the Cd 2+ adsorption process. Similar results have been
reported by Senthilkumaar et al. [45] for Cd 2+ removal using waste fruit
residues (orange, aplle, pineapple, dates, grape, etc). In this case, the removal
efficiency of phosphate-modified fruit residues was higher than the non-
modified waste fruit residue, especially at low pH values. Thus, the addition of
phosphate groups enhanced the adsorption capacity of the adsorbent.
Maple sawdust was examined as adsorbent for the Cd 2+ adsorption from
water by Rahman and Islam [48]. According to the parameters of the
Langmuir isotherm, the maximum Cd 2+ ions adsorption capacity onto maple
sawdust was found to be 7.4 mg g -1 .
Untreated Pinus halepensis sawdust was investigated as an adsorbent for
the removal of Cd 2+ from aqueous solution by Semerjian [4]. They observed
that the optimum pH was 9 and, at this condition, an adsorbent capacity of 10
g L -1 was determined. It took 30 min to remove cadmium almost completely
from a 5 mg L -1 cadmium solution. The kinetic of the cadmium adsorption was
very well described by a pseudo-second-order kinetic model.
Fixation of heavy metals ions onto P. sylvestris sawdust was investigated
by Taty-Costodes et al. [49]. The capacity of Cd 2+ removal was 96%. The
sorption followed a pseudo second order kinetics. The adsorption increased
with the pH and reached its maximum at a pH 5.5 solution.
Vázquez et al. used formaldehyde pretreated Pinus pinaster bark to sorb
Cd 2+ from aqueous solution [50]. Formaldehyde-treated P. pinaster bark
showed good affinity for Cd 2+ .The Cd 2+ sorption was almost total for Cd 2+ -
rich solutions with initial pH ≥ 6. They observed that the adsorption
mechanism was based on the Cd 2+ exchange by the protons ions from the ring
B of the procyanidin units present in tannins bark.
Cd 2+ ions adsorption, onto formaldehyde treated sawdust of sissoo wood
( Dalbergia sissoo ), was studied by Ahmad et al. [51]. The percent adsorption
of Cd 2+ ions increased with the pH, temperature and dosage of treated sawdust.
The adsorption capacity increased from 44.5 to 85.2 mg g -1 when the
temperature was increased from 25 to 60 ºC. Thermodynamic studies confirm
that the process was spontaneous and endothermic.
Ghodbane et al investigated the efficiency of the eucalyptus bark as a low
cost adsorbent for removing cadmium ions from aqueous solution [52]. The
maximum cadmium uptake was 14.53 mg g -1

at 20 ºC. The monolayer